1. Technical Field
The presently disclosed subject matter relates to a vehicle lamp such as a headlamp, an auxiliary light, a fog lamp, or other light which is composed of a light source unit using a plurality of point or line light sources and possibly a convex lens. Also, the presently disclosed subject matter relates to a vehicle headlamp which has a daytime running light function.
2. Description of the Related Art
Vehicle lamps using a light guide plate have been known heretofore. Examples thereof include a vehicle lamp or a headlamp as disclosed in Japanese Translation of PCT Patent Application No. 2006-509343 (corresponding to WO 2004/052682 or US 2006044825A1), and a common projector type headlamp as disclosed in Japanese Patent Application Laid-Open No. 2001-076510.
FIG. 1 shows the configuration of the vehicle lamp as disclosed in Japanese Translation of PCT Patent Application No. 2006-509343.
In FIG. 1, the vehicle lamp 1 can include a housing 2, a light-transmitting cover member 3, a light guide plate 4, a light source 5, and a reflection plate 4d (see also FIG. 2). The housing 2 has an opening 2a configured to emit light therethrough. The light-transmitting cover member 3 has a light incident surface 3a and a light emission surface 3b, and is fixed to the housing 2 so as to enclose the opening 2a of the housing 2. The light guide plate 4 is formed in a plate-like shape and is disposed inside the housing 2. With reference to FIG. 2, the light guide plate 4 has a light incident surface 4a configured to let light in, formed on a lateral side, and a light emission surface 4b formed on the front side facing toward the cover member 3. The light guide plate 4 is also provided with a scatter pattern 4c configured to scatter the light incident on the light incident surface 4a toward the light emission surface 4b. The light source 5 is arranged next to the light incident surface 4a of the light guide plate 4, and emits light toward the light incident surface 4a. The reflection plate 4d is arranged on the rear surface of the light guide plate 4, and can reflect light toward the front side of the light guide plate 4.
The light incident surface 3a and/or the light emission surface 3b of the cover member 3 can have lens patterns 3c configured to impart a certain pattern to emission light.
In this vehicle lamp 1, as shown in FIG. 2, the light emitted from the light source 5 can enter the light guide plate 4 through the lateral side (light incident surface) 4a. Traveling through the interior of the light guide plate 4 with total reflections, the light is scattered by the scatter pattern 4c formed on the rear surface of the light guide plate 4, and is projected from the front side (light emission surface) 4b of the light guide plate 4.
The light emitted in front of the light guide plate 4 illuminates the front area in a desired pattern through the cover member 3 which has the lens patterns 3c. 
The light source 5 can include a plurality of light emitting diodes (LEDs). A lens or other member can be arranged in front of this light source 5 in order to provide a desired light distribution characteristic.
FIG. 3 shows the configuration of the common projector type headlamp as disclosed in Japanese Patent Application Laid-Open No. 2001-076510. The headlamp 6 can include a light bulb 7 serving as a light source, a reflector 8, a projection lens 9, and a shielding member 9a. 
The reflector 8 can include an elliptic reflection surface having a first focus (rear side focus) where the bulb 7 is disposed and a major axis horizontally extending forward in the direction of light illumination. The inner surface thereof can serve as the reflection surface.
The projection lens 9 includes a convex lens, such as an aspheric lens, having a light-source side focus (rear side focus) at or near which the shielding member 9a is disposed.
The shielding member 9a is configured to impart a light distribution pattern for forming a low beam pattern of light emitted forward in the direction of light illumination. The shielding member 9a can include an upper edge with a predetermined shape configured to form a cutoff line in the light distribution pattern.
In the headlamp 6 configured as described above, light emitted from the bulb 7 can form a high luminous image (a high brightness image or a collected light image) having an inverted light distribution pattern (horizontally and vertically inverted) near the focus 9b of the projection lens 9 directly or after being reflected by the reflector 8. This high luminous image can be projected forward in the direction of light illumination while reversed by the projection lens 9.
In this case, part of the high luminous image can be shielded by the shielding member 9a so that a cutoff line C can be formed by the upper edge of the shielding member 9a (see FIG. 4). Then, the high luminous image can be projected forward as a low beam
It should be noted that the light distribution pattern shown in FIG. 4 for a right-side traveling vehicle has the cutoff line C for illuminating light also the area on the right-upper side.
In this case, the reflector 8 has a deformed elliptic cross section in order for light emitted from the bulb 7 to enter the projection lens 9 as much as possible. The bulb 7 is disposed near the one focus of the ellipse and the light incident surface of the projection lens 9 is disposed near the other focus of the ellipse. Accordingly, by properly designing the shape of the reflector 8, various light distribution patterns can be formed in accordance with the intended applications.
In the vehicle lamp 1 as disclosed in Japanese Translation of PCT Patent Application No. 2006-509343, light is scattered with the scatter pattern 4c before taken out of the light guide plate 4. Accordingly, the illuminated light can have a proper directional characteristic near the complete scattered light. The lens pattern 3c as used herein, thus, might not provide a suitable light distribution pattern having a desired luminous intensity as a vehicle light such as a headlamp and a vehicle auxiliary lamp such as a fog lamp, or having a bright-dark boundary.
Furthermore, a light distribution pattern can be formed by a plurality of separate lens patterns 3c. This can complicate the optical configuration of each individual lens pattern 3c. For example, some lens patterns are irradiated with the scattered light of the light guide plate 4 from peripheral areas other than the focal position. This can make it difficult to produce a given distribution pattern or cutoff line forward through the lens patterns 3c. 
The projector type headlamp as disclosed in Japanese Patent Application Laid-Open No. 2001-076510 uses the reflector 8 as in the previous case. This kind of reflector 8 can form a light distribution pattern near the focus 9b of the projection lens 9, which is then projected onto a road by the projection lens 9. Accordingly, in some cases the headlamp 6 can include the shielding member 9a inside the lamp. This can enlarge the headlamp 6 as a whole, resulting in increased weight and enlarged depth.
Furthermore, the reflector 8 used in this type of headlamp 6 should be designed in accordance with a desired shape of the light emitting portion of a bulb 7. This can increase the time required for designing such a reflector.